Direct conversion receiver for 2- and 4-level FSK signals

Direct conversion (DC) receivers are suitable for integrated circuit implementation. In this report, DC receivers for 2- and 4-level FSK signals are proposed and its BER performance is investigated with computer simulation. For FSK signals, a difference of baseband signal level appears as a difference in a velocity of rotation on IQ-plane. In the proposed circuits, this difference in the velocity is detected with differential circuits and logic circuits such as flip-flop, counter and so on. Performance under frequency offset is also investigated and a compensation method for the frequency offset is proposed.